CZ is very hard to distinguish from a real diamond, using the naked eye, at least, but the advantage with the is that is you get a D color, IF, in the 0.01>5.00 carat range, it's hard to tell the difference between them both, and they can often be cheaper (though they are sold at a price similar to diamond). The only advantage with CZ is that you can make stones that are up to 100 carats in size, and that is the only way that someone would know that it is a CZ (because a 100 carat diamond is hard to find)